In the production of silicon crystals grown by the continuous Czochralski method, polycrystalline silicon is melted within a crucible of a crystal growing device to form a silicon melt. A seed crystal is then lowered to the melt and slowly raised back up, solidifying the melt onto the seed crystal. Multiple crystals can be grown using a single crystal growing device with additional polycrystalline material added during the process. However, impurities concentrate over time in the melt from metal impurities in the feed polycrystalline silicon, impurities in a crucible of the crystal growing device, and impurities from other components within the crystal growing device such as a carbon susceptor, heater, and/or other components. When impurities reach an unacceptable level, the continuous Czochralski process is stopped, as crystals grown from the melt include impurities which reduce the minority carrier lifetime of the crystal. Typically, to remove the contaminated melt, the crystal growing device is cooled. As a result of the cooling, the melt freezes and destroys the crucible containing the melt. The crucible is replaced and other components are cleaned, aligned, and assembled.
Alternatively, the contaminated melt can be extracted while in a liquid or semi-liquid state. Extraction of the melt allows for removal of the concentrated impurities and for continued use of crystal growing device without requiring replacement of run kit components, such as crucibles and other consumable components. Some known melt extraction devices use a vessel lowered into a melt housing assembly that contains the melt to be removed. The melt extraction device removes the melt using a vacuum. The melt travels up a vacuum tube and enters a cavity defined by a housing of the melt extraction device. The vacuum is provided using a bellows in connection with a vacuum port and the vessel. Known bellows do not satisfactory address buckling of the bellow.
Due to the nature of long travel distances, such as 58.75 inch or longer, the use of expansion bellows as a vacuum channel in a melt extraction application results in a bellows that can buckle easily, e.g., if the bellows itself is unguided. A buckled bellow can result in a leak in the vacuum channel and partial or complete loss of vacuum provided by the bellow. As a result, the extraction device operates at reduced efficiency or ceases to operate. With complete or partial loss of vacuum due to buckling of the bellow, the melt extraction device may not be capable of extracting the melt.
This Background section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present disclosure, which are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present disclosure. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.